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Evolution and Development of Marine Biota in the Paleozoic As Affected by Abiotic Factors



Considering the development of biota in relation to changing abiotic factors shows that long intervals without sharp environmental changes, under transgression, active hydrodynamics, and a diversity of ecological niches, favor increases in the biodiversity of organisms. The reduction of biota is caused by quick changes in conditions, especially by multiple alternations of opposite trends (transgression – regression, warming – cooling, etc.). Moreover, negative effects arise from events expressly adverse for the development of organisms, such as the global development of anoxia in the oceans, powerful outflow of trap basalts and volcanism, and collisions of the Earth with cosmic bodies. The effects of various factors are identified especially vividly during biotic crises. Abiotic factors of the development of biota are predetermined by three fundamental causes – terrestrial (tectonics, volcanism), orbital, and cosmic. In many cases, these causes and factors predetermined by them operated simultaneously or were closely spaced on the geologic timeline. Since the cause-effect relation between them is definitely absent, we may assume that large-scale changes in the Earth's natural environment are caused by more general cosmic factors that are outside the limits of the solar system.
It was shown that the history of the biosphere is closely related to processes caused by low solar luminosity. Solar radiation is insufficient to maintain the Earth’s surface temperature above the freezing point of water. Positive temperatures are kept owing to the presence of greenhouse gases in the atmosphere: CO2, CH4, and others. Certain stages in the development of the biosphere and climate are related to these effects. Methane was the main carbon-bearing gas in the primordial atmosphere. It compensated the low solar luminosity. Life originated under the reduced conditions of the early Earth. Methane-producing biota was formed. Methane remained to be the main greenhouse gas in the Archean. The release of molecular oxygen into the atmosphere 2.4 Ga ago resulted in the disruption of the established mechanism of the compensation of the low solar luminosity. Methane ceased to cause a significant greenhouse effect, and the content of carbon dioxide was insufficient to play this role. A global glaciation began and had lasted for approximately 200 million years. However, the increasing CO2 content in the atmosphere reached eventually a level sufficient for the compensation for the low solar luminosity. The glaciation period came to an end. Simultaneously, a conflict arose between the role of CO2 as a gas controlling the thermal regime of the planet and as an initial material for biota production. As long as the resource of biotic carbon was inferior to that of atmospheric CO2, the uptake of atmospheric CO2 related to sporadic increases in biologic production was insufficient for a significant change in the thermal regime. This was the reason for a long-term climate stabilization for 1.5 billion years. By 0.8 Ga, the resource of oceanic biota reached the level at which variations in the uptake of atmospheric CO2 related to variations in the production of organic and carbonate carbon became comparable with the resource of atmospheric CO2. Since then, an oscillatory equilibrium has been established between the intensity of biota development and climate-controlling CO2 content in the atmosphere. Glaciation and warming periods have alternated. These changes were triggered by various geologic events: intensification or attenuation of volcanism; growth, breakup, or migration of continents; large-scale magmatism; etc. A new relation between atmospheric CO2 and biotic carbon was established in response to the emergence of terrestrial biota and the appearance of massive buffers of organic carbon on land. The interrelation of the biosphere and climate changed.
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A problem of modifying the International stratigraphic scale is discussed, and the present state of the Phanerozoic geochronological scale is analyzed. It is suggested that both scales reflect a combined response of the Earth subsystems (tectonosphere, biosphere, hydrosphere, and others) to powerful cosmic impacts on our planet, an element of the Solar System. The proposed ideas are supported by a theoretical model allowing to relate epochs of mass extinction of living organisms to periods of bombarding the Solar System by galactic comets and to moments of big asteroid impacts on the Earth. The proposed geological time scale that is calibrated with proper allowance for distribution of gravitational potential in the Galaxy is comparable in accuracy with the Phanerozoic geochronological scale.
The late Frasnian rugose coral list includes 148 comparatively shallow and 10 deeper water (cephalopod facies) species. At the most, only 6 (4%) of the shallow water species survived the Frasnian/Famennian faunal break, whereas 3-4 (30 or 40%) of the deeper water species survived the same event. -from Author
The late Palaeozoic was marked by significant changes in atmospheric chemistry and biotic composition. Geochemical models suggest a marked increase and then decline of atmospheric oxygen and associated shifts in the concentration of carbon dioxide. Although the actual magnitude of these changes is uncertain, the pulse of oxygen concentration may have reached a maximum of 35% and then dropped to 15% (compared with the present 21%). This oxygen pulse may have influenced the evolution of major groups of organisms.